Networking
tags: - cocubes - technical - networking
Networking Concepts and Protocols
OSI model
From lowest to highest:
- Physical — bits, signals, cables.
- Data Link — frames, MAC addressing, switches.
- Network — packets, IP addressing, routing.
- Transport — ports, TCP/UDP, end-to-end delivery.
- Session — session control.
- Presentation — encryption, compression, translation.
- Application — user-facing network services.
Mnemonic from low to high: Please Do Not Throw Sausage Pizza Away.
For fast MCQs: routing = Network layer; MAC = Data Link; port number = Transport; HTTP/DNS = Application.
TCP versus UDP
| TCP | UDP |
|---|---|
| connection-oriented | connectionless |
| reliable, ordered byte stream | no delivery/order guarantee |
| acknowledgements, retransmission, flow/congestion control | lower overhead and latency |
| web pages, file transfer, mail | streaming, gaming, DNS commonly |
TCP three-way handshake: SYN → SYN-ACK → ACK.
IP addressing and subnetting
IPv4 has 32 bits. CIDR slash length gives network bits; host bits = 32 − slash length.
| Prefix | Host bits | Total addresses | Traditional usable hosts |
|---|---|---|---|
| /24 | 8 | 256 | 254 |
| /25 | 7 | 128 | 126 |
| /26 | 6 | 64 | 62 |
| /27 | 5 | 32 | 30 |
| /28 | 4 | 16 | 14 |
| /29 | 3 | 8 | 6 |
Traditional usable hosts = 2^hostbits − 2, excluding network and broadcast. Treat special /31 and /32 rules as exceptions unless specifically asked.
Example: mask 255.255.255.224 = /27. It leaves 5 host bits, so 30 traditional usable hosts/subnet.
Common protocols and ports
| Service | Purpose | Default port |
|---|---|---|
| HTTP | web | 80 |
| HTTPS | secure web | 443 |
| DNS | name to IP lookup | 53 |
| DHCP | IP configuration | UDP 67/68 |
| SSH | secure remote shell | 22 |
| FTP | file transfer control | 21 |
| SMTP | sending email | 25 |
| POP3 | retrieving email | 110 |
| IMAP | synchronised email access | 143 |
| Telnet | insecure remote terminal | 23 |
Essential services
- DNS translates domain names to IP addresses.
- DHCP dynamically provides IP configuration: address, mask, gateway, DNS.
- ARP maps an IPv4 address to a MAC address on a local network.
- NAT translates private internal addresses to public addresses.
- Router forwards between networks; switch forwards frames within a LAN.
HTTP status codes
| Code | Meaning |
|---|---|
| 200 | success |
| 201 | resource created |
| 301/302 | redirect |
| 400 | bad request |
| 401 | unauthenticated/credentials required |
| 403 | authenticated but forbidden |
| 404 | resource not found |
| 500 | server error |
Security basics
- Encryption protects confidentiality.
- Hashing provides one-way integrity/checking; hashes are not encryption.
- TLS protects HTTP traffic as HTTPS.
- Firewall filters traffic based on rules.
- VPN creates an encrypted tunnel over an untrusted network.
[[03_Technical/Technical_Drills|Technical drills]] · [[03_Technical/Technical_Quick_Recall|Quick recall]]